Abstract
A thorough understanding of the radiation balance over a crop canopy and the accurate estimation of different components of net radiation over the crop surface assume a great significance in terrestrial ecosystem. Considering its importance a field experiment was conducted at agricultural farm of GBPUA&T Pantnagar during rabi season of 2012-13 to estimate partitioning of energy balance components by using Bowen Ratio Energy Balance (BREB) method at different phenological stages of wheat. The BREB method was used to obtain field energy balance, including latent heat flux, soil heat flux. These measurements were coupled with radiation measurement at the soil surface to partition energy balance component at different phenological stages of wheat viz. Crown root initiation (CRI), tillering, jointing, heading, flowering, grain filling, soft dough and hard dough stage .It was found that net radiation (Rn) was the major portion of energy balance component. The values varied between 6.02 to 27.6 MJm -2 d -1 at various growth stages of wheat crop. Similarly, latent heat flux (LE) ranged between 2.11 to 12.79 MJm -2 d -1 during the crop season. In the present study in different phenological stages of wheat, latent heat flux varied between 3.59 to 15.25 MJm -2 d -1 . The ground heat flux varied from 0.31 to 0.88 MJm -2 d -1 in different stages. The peak midday ground heat flux decreased gradually from crown root initiation to soft dough stage because of increasing soil coverage. It can be concluded from the present study that Bowen ratio approach is an efficient technique of measurement of energy balance. This method, as applied, can accurately estimate energy balance component for wheat crop in Tarai region of Uttarakhand. Key word: Latent heat flux(LE), Phenological stages, Crown root initiation, Net radiation, Soft dough stage, BREB method I. Introduction Radiation and latent and sensible heating are among the most important processes in land-atmosphere exchanges. Hence, quantitative understanding and accurate estimation of these fluxes at large scales are imperative for research and applications in areas ranging from climate research, water cycle study, to water resources management, sustainable agricultural production and ecological conservation. The quantity and the form of energy available in a system determine the efficiency of the system. Available net radiation is the main source of energy in the earth system. Total energy available over a crop surface and partitioning of this into different components such as sensible heat (H), latent (LE) and soil heat fluxes (G) determine the crop production. Therefore, a thorough understanding of the radiation balance over a crop canopy and the accurate estimation of different components of net radiation over the crop surface assume a great significance in terrestrial ecosystem. The components of energy balance are calculated with the of help Bowen-ratio energy balance method and energy balance equation (Rn+ H +LE +G+PS+M =0). `
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